Pre-existing cognitive impairment and post-operative cognitive dysfunction: should we be talking the same language?

Changes in cognition are known to follow anesthesia and surgery in older individuals (Evered et al., 2011). Although survival per se was the prime outcome in the 19th and early 20th centuries for invasive procedures, a link was none-the-less observed with adverse cognitive outcomes as far back as 1887 (Savage, 1887). Historical reports of "insanity" or "weak mindedness" after anesthesia appeared within 40 years of the first anesthetic having been administered and anecdotal and retrospective reports have implicated anesthesia ever since. However, it was not until the 1970s that these observations received any sound scientific evaluation, when clinicians became aware of cognitive changes following cardiac surgery. It was assumed that the cardiopulmonary bypass (heart lung machine) must have been the main culprit because it was this factor which so greatly distinguished cardiac surgery from non-cardiac surgery (Shaw et al., 1987). This long held belief entered surgical folklore and was the basis for many publications endeavoring to identify particular aspects of the heart lung machine responsible for this cognitive decline.